I used to be a youth leader with a DA of the C&CC and used to take 20 or so kids of 12 and over away camping. I beleve you have to be sensible and you have to be aware of potential problems but you have to put them into perspective.
I cannot see that there is any substantiated risk in allowing children over the age of 12, or possibly 10 if there are more than one, sleeping in the awning either in a bedroom annex or internal tent in the awning. Kids have also been sleeping in pup tents for generations.
I cannot see the difference in a child sleeping in the awning and a child in its own bedroom in a large family tent. If your worried leave the van door open.
I was once on the organising committee of a large ralley held by the C&CC. The vans were parked back to back and there were pup tents down the middle between them. It would have been impossible for a car to get in between the vans but we hadn't counted on a motor bike. A local lad used the field as a short cut every night, and on entering the field in the dark, and seeing lots of vans on his normal route across the field, went between the vans and run into a pup tent with 2 or 3 kids in it. There was no injuries but a lot of commotion as the bike became tangled with the tent.I don't know point I am making but you cannot worry about everything and children have to become independant.